/****************************************************************************
 *
 * Copyright 2023 Samsung Electronics All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied. See the License for the specific
 * language governing permissions and limitations under the License.
 *
 ****************************************************************************/
/****************************************************************************
 * arch/arm/src/armv7-a/arm_vfork.c
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <tinyara/config.h>

#include <inttypes.h>
#include <stdint.h>
#include <string.h>
#include <assert.h>
#include <errno.h>
#include <debug.h>

#include <tinyara/sched.h>
#include <tinyara/arch.h>
#include <arch/irq.h>

#include "arm_vfork.h"
#include "up_internal.h"
#include "sched/sched.h"

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: up_vfork
 *
 * Description:
 *   The vfork() function has the same effect as fork(), except that the
 *   behavior is undefined if the process created by vfork() either modifies
 *   any data other than a variable of type pid_t used to store the return
 *   value from vfork(), or returns from the function in which vfork() was
 *   called, or calls any other function before successfully calling _exit()
 *   or one of the exec family of functions.
 *
 *   The overall sequence is:
 *
 *   1) User code calls vfork().  vfork() collects context information and
 *      transfers control up up_vfork().
 *   2) up_vfork() and calls nxtask_setup_vfork().
 *   3) nxtask_setup_vfork() allocates and configures the child task's TCB.
 *      This consists of:
 *      - Allocation of the child task's TCB.
 *      - Initialization of file descriptors and streams
 *      - Configuration of environment variables
 *      - Allocate and initialize the stack
 *      - Setup the input parameters for the task.
 *      - Initialization of the TCB (including call to up_initial_state())
 *   4) up_vfork() provides any additional operating context. up_vfork must:
 *      - Initialize special values in any CPU registers that were not
 *        already configured by up_initial_state()
 *   5) up_vfork() then calls nxtask_start_vfork()
 *   6) nxtask_start_vfork() then executes the child thread.
 *
 * nxtask_abort_vfork() may be called if an error occurs between steps 3 and
 * 6.
 *
 * Input Parameters:
 *   context - Caller context information saved by vfork()
 *
 * Returned Value:
 *   Upon successful completion, vfork() returns 0 to the child process and
 *   returns the process ID of the child process to the parent process.
 *   Otherwise, -1 is returned to the parent, no child process is created,
 *   and errno is set to indicate the error.
 *
 ****************************************************************************/

pid_t up_vfork(const struct vfork_s *context)
{
	struct tcb_s *parent = this_task();
	struct task_tcb_s *child;
	uint32_t newsp;
	uint32_t newfp;
	uint32_t newtop;
	uint32_t stacktop;
	uint32_t stackutil;

	svdbg("vfork context [%p]:\n", context);
	svdbg("  r4:%08" PRIx32 " r5:%08" PRIx32 " r6:%08" PRIx32 " r7:%08" PRIx32 "\n", context->r4, context->r5, context->r6, context->r7);
	svdbg("  r8:%08" PRIx32 " r9:%08" PRIx32 " r10:%08" PRIx32 "\n", context->r8, context->r9, context->r10);
	svdbg("  fp:%08" PRIx32 " sp:%08" PRIx32 " lr:%08" PRIx32 "\n", context->fp, context->sp, context->lr);

	/* Allocate and initialize a TCB for the child task. */

	child = task_vforksetup((start_t)(context->lr & ~1));
	if (!child) {
		sdbg("ERROR: task_vforksetup failed\n");
		return (pid_t)ERROR;
	}

	svdbg("TCBs: Parent=%p Child=%p\n", parent, child);

	/* How much of the parent's stack was utilized?  The ARM uses
	 * a push-down stack so that the current stack pointer should
	 * be lower than the initial, adjusted stack pointer.  The
	 * stack usage should be the difference between those two.
	 */

	stacktop = (uint32_t)parent->stack_base_ptr + parent->adj_stack_size;
	DEBUGASSERT(stacktop > context->sp);
	stackutil = stacktop - context->sp;

	svdbg("Parent: stackutil:%" PRIu32 "\n", stackutil);

	/* Make some feeble effort to preserve the stack contents.  This is
	 * feeble because the stack surely contains invalid pointers and other
	 * content that will not work in the child context.  However, if the
	 * user follows all of the caveats of vfork() usage, even this feeble
	 * effort is overkill.
	 */

	newtop = (uint32_t)child->cmn.stack_base_ptr + child->cmn.adj_stack_size;

	newsp = newtop - stackutil;

	/* Move the register context to newtop. */

	memcpy((void *)(newsp - XCPTCONTEXT_SIZE), child->cmn.xcp.regs, XCPTCONTEXT_SIZE);

	child->cmn.xcp.regs = (void *)(newsp - XCPTCONTEXT_SIZE);

	memcpy((void *)newsp, (const void *)context->sp, stackutil);

	/* Was there a frame pointer in place before? */

	if (context->fp >= context->sp && context->fp < stacktop) {
		uint32_t frameutil = stacktop - context->fp;
		newfp = newtop - frameutil;
	} else {
		newfp = context->fp;
	}

	svdbg("Old stack top:%08" PRIx32 " SP:%08" PRIx32 " FP:%08" PRIx32 "\n", stacktop, context->sp, context->fp);
	svdbg("New stack top:%08" PRIx32 " SP:%08" PRIx32 " FP:%08" PRIx32 "\n", newtop, newsp, newfp);

	/* Update the stack pointer, frame pointer, and volatile registers.  When
	 * the child TCB was initialized, all of the values were set to zero.
	 * up_initial_state() altered a few values, but the return value in R0
	 * should be cleared to zero, providing the indication to the newly started
	 * child thread.
	 */

	child->cmn.xcp.regs[REG_R4] = context->r4;	/* Volatile register r4 */
	child->cmn.xcp.regs[REG_R5] = context->r5;	/* Volatile register r5 */
	child->cmn.xcp.regs[REG_R6] = context->r6;	/* Volatile register r6 */
	child->cmn.xcp.regs[REG_R7] = context->r7;	/* Volatile register r7 */
	child->cmn.xcp.regs[REG_R8] = context->r8;	/* Volatile register r8 */
	child->cmn.xcp.regs[REG_R9] = context->r9;	/* Volatile register r9 */
	child->cmn.xcp.regs[REG_R10] = context->r10;	/* Volatile register r10 */
	child->cmn.xcp.regs[REG_FP] = newfp;	/* Frame pointer */
	child->cmn.xcp.regs[REG_SP] = newsp;	/* Stack pointer */

#ifdef CONFIG_LIB_SYSCALL
	/* If we got here via a syscall, then we are going to have to setup some
	 * syscall return information as well.
	 */

	if (parent->xcp.nsyscalls > 0) {
		int index;
		for (index = 0; index < parent->xcp.nsyscalls; index++) {
			child->cmn.xcp.syscall[index].sysreturn = parent->xcp.syscall[index].sysreturn;

			/* REVISIT:  This logic is *not* common. */

#if defined(CONFIG_ARCH_ARMV7A_FAMILY)
#ifdef CONFIG_BUILD_PROTECTED

			child->cmn.xcp.syscall[index].cpsr = parent->xcp.syscall[index].cpsr;

#endif

#elif defined(CONFIG_ARCH_ARMV7R)
#ifdef CONFIG_BUILD_PROTECTED

			child->cmn.xcp.syscall[index].cpsr = parent->xcp.syscall[index].cpsr;

#endif
#elif defined(CONFIG_ARCH_ARMV6M) || defined(CONFIG_ARCH_ARMV7M) || \
      defined(CONFIG_ARCH_ARMV8M)

			child->cmn.xcp.syscall[index].excreturn = parent->xcp.syscall[index].excreturn;
#else
#error Missing logic
#endif
		}

		child->cmn.xcp.nsyscalls = parent->xcp.nsyscalls;
	}
#endif

	/* And, finally, start the child task.  On a failure, nxtask_start_vfork()
	 * will discard the TCB by calling nxtask_abort_vfork().
	 */

	return task_vforkstart(child);
}
